1. Field
One embodiment of the present invention relates to a telephone system which implements voice communication between terminals by using a protocol such as Media Gateway Control (Megaco) or Session Initiation Protocol (SIP), and a terminal device in the system.
2. Description of the Related Art
So called Voice over IP (VoIP) which is a technique for performing voice communication by using an Internet Protocol (IP) network has reached the mainstream of current telephone systems. A personal computer, personal digital assistant (PDA), or the like can be used as a telephone by installing a VoIP function in it and connecting it to a local area network (LAN). A system of this type controls outgoing/incoming operation on the basis of IP addresses, and hence can easily relocate a telephone terminal. For example, Jpn. Pat. Appln. KOKAI Publication No. 2005-260419 discloses a technique based on the assumption of the movement of a terminal.
With upgrading of the system, software in a terminal is often updated. In, for example, a cellular phone system, the function of a user terminal is sometimes updated by downloading a new application from a server to the terminal by a push system. A minor function change can be made by such a technique without any problem.
In a case in which a protocol which controls an overall system is to be updated or a case in which a server apparatus functions as the backbone of services is to be replaced, a terminal device is sometimes changed up to a level near hardware layer by updating its firmware entirely.
In this case, a problem arises when the relation between the new and old systems is lost. That is, when the firmware of a terminal device connected to an old main unit is updated to firmware for a new main unit, the terminal after update cannot communicate with the main unit of the old system. As a result, for example, problems A and B arise.
(A) The firmware of a terminal is updated by operation from the old system. After the update, since the terminal is connected to only the new system instead of the old system, the operator of the old system cannot determine whether the firmware has been updated normally.
(B) If the terminal after the completion of firmware update cannot be connected normally to the new system due to some kind of abnormality, the terminal is connected to neither the new system nor the old system. This makes it impossible to do recovery work.
As described above, in existing telephone systems, in a case in which the main unit at the connection destination is to be replaced after the firmware of a terminal is updated, it is impossible to check the normality of update or to recover from an update failure. This poses problems in operation.